JPH0796128A - Single floor pressure variation type adsorption system and method - Google Patents

Abstract

PURPOSE: To recover product oxygen at increased flow rate using a pressure swing adsorption apparatus and to enhance adsorption capacity of the single bed of adsorbent materials by performing pressurizing/product recovering, partially pressure-reducing, vacuum-exhausting, purging and partially re-pressurizing. CONSTITUTION: Supply air is introduced from a pipe line 1 to the bottom of the single adsorption bed 19 in an adsorption vessel using a blower unit 2 used commonly as a supply blower/vacuum blower and product oxygen is stored in a product surge tank 26 for using afterward at the pressurizing/product recovering stage, void space gas is recovered in an equalization tank 23 at the partially pressure-reducing stage, the desired amount of product oxygen is supplied from the tank 26 to the bed 19 as purge gas at the vacuum- exhausting stage, and the void space gas recovered in the tank 23 is supplied to the bed 19 at the partially re-pressurizing stage.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a pressure swing adsorption method and apparatus for air separation, and more particularly to the use of a single bed pressure swing adsorption system for the recovery of oxygen from air. To do.

[0002]

2. Description of the Related Art Pressure change adsorption (PSA, pressure swi
ng adsorption) process and system for separating and purifying at least one component from a feed gas mixture comprising at least one non-adsorbable component and at least one readily adsorbable component. Provide an industrially attractive means. Adsorption occurs at an upper adsorption pressure within the adsorbent bed, and the readily adsorbable components adsorbed to the adsorbent are then desorbed from the adsorbent bed by reducing the adsorbent bed pressure to the lower desorption pressure. Adsorption / desorption PS
The A process is well known and relates to, for example, PSA systems having four or more beds, U.S. Pat.
No. 418. As disclosed in this patent, the PSA process is based on the periodic switching of multiple beds of four or more beds, in each bed, (1) introducing a feed gas at the feed end of the bed and producing the bed. Feed gas to the pressure adsorption stage at the upper adsorption pressure to release components that are not easily adsorbed as product gas from the product discharge end, and (2) to intermediate pressure by the release of void gas from the product discharge end of the bed. (3) a decompression stage in the same direction as the flow, and (3) a decompression stage in the flow opposite to the feed gas to a lower downward desorption pressure by releasing components that can be easily adsorbed from the feed end of the bed, (4) ) An optional purge (scavenging) step at its lower desorption pressure, through which purge gas is passed through the product discharge end of the bed and exhausted from the feed end of the bed of readily adsorbable components desorbed from the bed. Purging phase to improve It is performed from the lower desorption pressure as may be repeated with an additional amount of feed gas being passed in process sequence steps that include the re-pressurization phase of upward adsorption pressure. The void gas released during the depressurization stage co-current with the feed gas is generally used for pressure equalization purposes between beds in a multi-bed system and to provide purge gas to the beds at lower desorption pressure. Variations on these process sequence steps are also used in the art for use in systems containing one or more adsorbent beds.

In many chemical refining processes, metal production and other industrial applications, high purity gas streams are often used for various purposes. For example, high purity oxygen is used in various industries such as chemical processing, steelmaking, papermaking, and in lead and glass manufacturing operations. Many such applications require oxygen purities in the 90-93% range at flow rates up to 3000 m ³ / hr and above. The PSA process is well suited for air separation for producing oxygen and nitrogen by virtue of a combination of the various process steps mentioned above and by variants thereof, especially in comparisons which a cryogenic air separation plant cannot carry out industrially. Suitable for small-scale operation. In a PSA system for the purpose of recovering high-purity oxygen as a component in the air that cannot be easily adsorbed, the adsorption bed selectively adsorbs nitrogen as an easily adsorbable component in the air. It contains a possible adsorbent material, where nitrogen is desorbed and withdrawn from the bed upon depressurization of the bed pressure to a lower desorption pressure as the cyclic adsorption / desorption sequence steps are carried out in the PSA system.

In PSA-oxygen recovery and other PSA processing applications, it is desirable to minimize equipment design, fabrication, transportation and equipment costs in order to achieve reduced investment costs and increased system reliability. Therefore, it is desirable to use PSA systems and processes that minimize the number of adsorbent vessels, adsorbent storage vessels, associated tanks, valves, compression equipment, process lines and other operating components. P
The costs associated with operating an SA system are minimized by the use of processes that require less power per unit of product produced. It is desired that such processes for oxygen production exhibit a high recovery of oxygen from the feed air while at the same time allowing the use of low compression ratios in the associated compression equipment.

PSA systems containing more than three adsorbent beds, as in the patents cited above, are particularly useful for certain gas separation operations to achieve high volume, high purity and high recovery performance. Desired. For other applications, 2-3 bed PS
It is possible and desirable to use the A system. For example, it has been found desirable to use a two-bed PSA system for a variety of practical industrial PSA oxygen production applications. For example, a two-bed vacuum pressure swing adsorption (VPSA) system has been proposed. The inlet gas mixture to be separated is usually compressed to a high pressure, usually a few atmospheres, before the desired selective adsorption takes place. The resulting high pressure product, for example oxygen with a low selective adsorption of the feed air, is passed through a pipeline for downstream use. In a typical two-bed PSA operation, transition pressure conditions around atmospheric pressure are used. Thus, part of the cycle is carried out above atmospheric pressure and part is carried out below atmospheric pressure. Separation is done at pressures very close to 1 atmosphere and the product is then compressed to the desired downstream pressure. This has been considered to be a cost-saving mode of operation since the required gas compression is essentially only on the product stream, not on the total incoming feed gas stream. But this PS
Since the A process cycle involves both pressure and vacuum (vacuum) conditions, two machines are required to perform the cycle: a feed pressure blower and a vacuum blower. Such a two-bed system is 20,000 to 50,000
0 NCFH (560 to 1400 m ³ / hour: standard condition)
Cost savings can be achieved for oxygen plant equipment in the range of oxygen production scales up to and above. However, for applications with flow requirements below this range, the investment costs associated with a two-bed vacuum pressure swing adsorption system make such a process unprofitable.

A single bed, single machine (blower) embodiment of the VPSA system has been proposed in the art to make the VPSA system suitable for lower flow applications. VP
Most of the investment costs associated with SA-oxygen plants are
Investment costs are included in the system, whether it is for fiber operations that change pressure to around atmospheric pressure, or for systems where vacuum conditions are not used, as it relates to air blowers, process vessels and adsorbents used in these vessels. It will be appreciated that significant savings can be achieved by cutting the number of blowers and the number of adsorbent vessels contained in half.

A single bed PSA system is disclosed in US Pat.
61,865. In this method, the pressure control valve in the discharge line from the top of the adsorption bed opens when the pressure in the top of the single process vessel is at a certain level.
The gas is passed directly to the external equalization tank in the discharge line. In the embodiment of this patent, there is a bypass line at the outlet of the pressure control valve, including the check valve, separate from the discharge line and connected to the product surge tank. When the pressure in the product surge tank equals the pressure in the equalization tank, the check valve opens and product gas is simultaneously supplied to the equalization tank and the product surge tank. A check valve blocks the return flow from the product surge tank to the adsorbent bed when the bed pressure falls below that of the product surge tank. In this arrangement, the equalization tank acts as an extension of the product surge tank. This is because both tanks are pressurized to the same maximum pressure and contain the same purity of gas. This patent also teaches the use of a blowdown stage to partially depressurize the adsorption vessel prior to evacuation.

[0008]

This patent describes a single bed P
While addressing the need in the field for SA systems, such single bed operations require additional improvements before they can meet the need for low flow applications. To do. In particular, a higher product flow rate is desired as compared to the product flow rates obtained with the system of the above patent and other such single bed PSA systems. The object of the present invention is to
It is to develop an improved low volume PSA method and apparatus for oxygen recovery from air for low volume applications.
Yet another object of the present invention is to develop an improved single bed PSA process and apparatus for low volume recovery of oxygen from air. Yet another object of the present invention is a single bed, low volume PSA for increasing the flow rate of product oxygen recovered from air.
To develop a method and apparatus.

[0009]

The present invention provides a product surge tank as a means of supplying product oxygen and a purge gas to the adsorbent bed, and a void gas to the bed for bed repressurization purposes. The problem is solved by making good use of the functioning equalizing tank. The present invention comprises: (a) passing feed air through the feed end of a single bed of adsorbent material capable of selectively adsorbing nitrogen as an easily adsorbable component of the air, and controlling the pressure within the bed. Increasing from an intermediate pressure to an upper adsorption pressure and passing oxygen as a non-adsorbable component of the air from the product end of the bed through a product surge tank at a pressure close to said upper adsorption pressure; ) Depressurizing the bed to an intermediate pressure in the same direction as the feed air flow by releasing void gas from the product end of the bed and passing the void gas through an equalization tank; (c) from the bed feed end. Depressurizing the bed from an intermediate pressure to a lower desorption pressure in the opposite direction of the feed air flow by releasing an additional amount of gas of (d)
A sidestream of the product gas from the product surge tank is passed as a purge gas to the product end of the bed to purge desorbed nitrogen from the voids in the bed at the lower desorption pressure and to remove the desorbed nitrogen from the bed. Discharging from the supply end of
(E) introducing void gas from the equalization tank to the product end of the bed to increase the pressure in the bed from the lower desorption pressure to the intermediate pressure; and (f) supplying an additional amount. Air is passed through the feed end of the single bed and the steps (a)-
(E) continuing the cyclical operation, whereby product oxygen is recovered from air at an increased product flow rate to improve the adsorption capacity of a single bed of adsorbent material. Provided is a pressure change adsorption method for recovering oxygen from air. The invention also relates to (a) a single bed of an adsorbent material capable of selectively adsorbing nitrogen as a readily adsorbable component of air, and (b) a product end of said bed which is discharged. To an equalization tank for holding a void gas, (c) a product surge tank for holding a product oxygen released from the product end of the bed, and (d) an equalizing tank for a void gas. And (e) a flow of void gas to the equalization tank and a flow of product oxygen to the product surge tank and a void gas equalization. Control means for controlling the flow from the liquefaction tank to the bed product end and the side flow of product oxygen from the product surge tank to the bed product end, and (f) air feed end of the bed. Feed blower means for passing through (g) from the feed end of the bed Conduit means for releasing interstitial gas and nitrogen, whereby product oxygen can be recovered at an increased product flow rate in a pressure swing adsorption device, and the adsorption capacity of a single bed of adsorbent material can be increased. There is also provided a pressure change adsorption device for the recovery of oxygen from air, which is characterized by an improvement.

[0010]

The objects of the present invention are accomplished using a single process machine, a single bed PSA to VPSA system which incorporates a compressor for pressurizing and depressurizing a single bed during a processing cycle. Conventional product surge tanks are used with equalization tanks that serve to improve the product recovery and power requirements of the system. That is,
The present invention utilizes a single floor P that utilizes two external surge tanks.
The SA to VPSA method and apparatus is used. One of the surge tanks supplies the desired product oxygen and also PS
Product oxygen is supplied as a purge gas to the adsorbent bed during the exhaust phase of the A-VPSA treatment cycle. The second surge tank functions as an equalization tank and collects the void gas withdrawn from the bed during the depressurization stage and feeds the void gas to the bed during the repressurization stage of the adsorbent bed. Used for. In practicing the invention, US Pat. No. 4,561,
A significant improvement in performance is achieved over prior art single bed PSA systems represented by No. 865.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, a line 1 is used to supply feed air to a combined blower / vacuum blower blower unit 2 and incorporates a dust filter-gas silencer unit 3 and a valve 4. . Line 5 from unit 2 is connected to lines 6 and 7. Line 6 includes a valve 8 and an outlet snubber (buffer tank) unit 9 from which gas is discharged through line 10. The pipe line 7 includes an outlet snubber (buffer tank) unit 11, an after cooler (second stage cooler) 12 for cooling the supply gas, and a valve 1.
3 is incorporated. Discharge line 14 incorporating valve 15
Is connected to the pipeline 7. Line 1 incorporating valve 17
6 is connected to line 1 downstream of valve 4. Both lines 7 and 16 lead to the bottom of a single adsorption bed 19 in a suitable adsorption vessel. From the top of the adsorbent bed 19, a line 20 extends and leads to a line 21 having a valve 22 and leading to an equalization tank 23, and a check valve 25 and leading to a product surge tank 26. 24 is also known. Product oxygen is withdrawn from product surge tank 26 via line 27 for its desired use in downstream operations. Line 20 also has a valve 29 and communicates with line 28 which extends to the surge tank 26.

PSA using the system illustrated in the drawings
In operating the process, a five stage process operating cycle is preferably used. Such a cycle includes the following process sequence steps: (1) pressurization / product recovery, (2).
Partial decompression, (3) vacuum exhaust, (4) purge and (5)
Partial repressurization.

In operation of the above process sequence steps, the first step is for the adsorbent bed 19 to have a pressure of about 10 psia (0.7 kg / c).
It begins shortly after being partially pressurized to an intermediate pressure of m ² ). Supply air opens valves 4 and 13 and opens valves 8, 15, 17, 2
It is supplied from the feed blower 2 with 2 and 29 closed. The check valve 25 is set to open when the pressure in the adsorption bed 19 exceeds the pressure in the product surge tank 26.

As the feed air is introduced into the vessel containing the adsorbent bed 19, the pressure in the vessel increases, eventually generating at 18 psia (1.26 kg / cm ² absolute pressure). A point equal to the pressure in the surge tank 26 is reached. Therefore, the check valve 25 is opened, and the product gas,
That is, oxygen is supplied to the product surge tank 26. The size of the product surge tank 26 will vary with the desired product flow and pressure in the outlet line 27, but will allow the product gas flow from the adsorbent bed 19 without significant pressure fluctuations, for example 4-5 psi ( 0.28~0.35kg / cm ²⁾ must be sufficiently large to accommodate within. The product surge tank 26 must also be able to allow a simultaneous purge flow from there back to the adsorbent bed 19 without interruption of product flow in line 27 during the purge phase. The product feed is such that the pressure at the top of the vessel for the adsorbent bed is above the adsorption pressure, typically 22.5 psia.
Continue until reaching (1.58kg / cm ² ). At this point, the process cycle proceeds to its second stage. Alternatively, the pressure control valve is replaced by a check valve and operated in such a manner as to maintain a constant vessel pressure during the product manufacturing portion of the cycle stage to further improve the process.

During the remaining stages of the process sequence, product surge tank 26 supplies product oxygen for downstream use independent of the vessel for adsorbent bed 19 or other process equipment associated therewith. You should bear in mind what to do. Typical stage time for the first stage in the process is 1
8 to 25 seconds. The temperature of the feed air may correspond to the ambient temperature, but generally the feed gas to the adsorbent bed 19 is 30-40F (20-22 ° C) above ambient temperature and the temperature distribution within the adsorbent vessel is within the vessel. At the bottom of the adsorbent level of about 10 to 20 ° F (5.5 to 11 ° F) above ambient temperature.
C.), about ambient temperature or up to 10 ° F. (5.5 ° C.) above ambient temperature in the middle of the adsorbent bed, and about 30-40 ° F. (20-22 ° C.) above the top of the adsorbent bed. These temperatures will vary slightly throughout the process sequence steps. The feed air flow rate used is directly related to the desired product flow rate. For 50% oxygen recovery at 90% product purity, the feed air flow rate is generally about 9.5 times greater than the corresponding oxygen product flow rate.

At the beginning of the second stage of the process sequence, partial decompression, valve 13 is closed and valve 15 is opened. This causes the supply blower 2 to be unloaded, i.e. sucking air from the atmosphere and returning it to the atmosphere and exhausting it. The valve 22 opens and the adsorbent bed 19 begins to depressurize from the upper adsorption pressure reached in the first stage of the process sequence. Void gas is rejected from the voids in adsorbent bed 19 and passed through line 21 to equalization tank 23.
The dimensions of this tank 23 can be varied depending on the desired equipment scale, ie product flow rate, but the void gas from the adsorbent vessel is approximately 14.5 to 15 psia (1.02 to 1.05 kg / c).
It must be large enough to hold at a pressure of m ² ). The concentration of oxygen in this tank is typically 85-89.
% Oxygen. The check valve 25 is closed because the pressure in the adsorbent bed 19 has dropped below the pressure in the product surge tank 26. During this process step, valves 8, 17 and 29 were kept closed, which was continued until the adsorbent bed vessel pressure had dropped to an intermediate pressure, eg 16 psia (1.12 kg / cm ² ), the equalization tank. The pressure in 23 is 14.5 ~
The pressure is increased to 15 psia (1.02 to 1.05 kg / cm ² ). The approximate cycle stage time for this second partial decompression stage is about 4-7 seconds. After this, the process sequence step proceeds to the third step. The temperature of the adsorbent bed 19 vessel during the second stage is similar to that previously mentioned in the first stage.

After the adsorbent bed 19 vessel has expelled some of the void gas into the equalization tank 23 and the adsorbent bed 19 vessel pressure has dropped to an intermediate pressure of about 16 psia (1.12 kg / cm ² ). The process cycle proceeds to the third stage of the process sequence stage, namely the container evacuation stage. For the purpose of the third stage, valves 8 and 17 are opened and valves 4, 15,
13, 22 and 29 and the check valve 25 are closed. As a result, the gas in the container of the adsorbent bed 19 is
Is diverted in the opposite direction through the bottom of the tank and flows through the valve 17 in line 16 to the inlet of the blower 2. This void gas is released to the atmosphere through the outlet silencer 9. This piping and valve arrangement allows the blower 2 to evacuate the vessel of the adsorbent bed 19 to a pressure below atmospheric pressure. The approximate composition of the exhaust gas averaged throughout the exhaust phase of this process cycle is 9
0% nitrogen and 10% oxygen. When the blower is used in exhaust applications, sealing water may be injected at the inlet of the blower to seal the gap in the lobes of the blower 2 in order to improve the combined performance with the blower. This water sealing means allows the blower to perform better in exhaust applications. When the vessel is evacuated to below atmospheric pressure, desorption from the surface of the adsorbent occurs due to the difference in the partial pressure of the nitrogen gas within the adsorbent's voids, thereby regenerating the adsorbent and producing it for downstream use. Place the adsorbent in a condition for re-adsorption of nitrogen from an additional amount of feed air to provide a semi-continuous flow of oxygen. In this container evacuation stage, the pressure inside the container is vacuum desorption pressure, for example, about 5 psia (0.3
Until a desired low desorption pressure, such as 5 kg / cm ² ) is reached. The stage time for this cycle stage is about 30-
40 seconds. The process cycle then proceeds to the fourth of the process sequence steps.

The fourth process stage is a vessel purge (scavenging) stage at a lower desorption pressure. For this purpose valve 2
9 is opened and a small amount of product gas sidestream from the product surge tank 26 is diverted to the top of the vessel in the single adsorption bed 19. This stream has an oxygen concentration of 90-93% and at this point is used to scavenge a majority of the residual void gas in the vessel, which is mainly composed of desorbed nitrogen. The purge gas stream replaces the desorbed gas present in the voids in the vessel, and since the purge stream does not have a high nitrogen concentration, the void gases are not re-adsorbed on the adsorbent surface as the pressure in the vessel begins to increase. This is because the adsorbent does not have a selective affinity for oxygen. This vessel purging phase occurs at a constant vacuum or at another desorption pressure level in the vessel, valves 8 and 17 remain open, control valve 29 is open and all other valves are closed. When most of the desorbed gas in the adsorbent bed voids in the vessel has been replaced by product gas, the process sequence step proceeds to the fifth process step, the partial repressurization step. The average time for the fourth vessel purge stage is about 7-1.
0 seconds. In order to maintain the vacuum level substantially constant for this vessel evacuation stage, the flow rate for the desorbed gas emerging from the vessel is, for example, 5 psia (0.35 kg / cm ² ).
At, the exhaust flow rate is made approximately equal to.

The fifth of the process sequence steps is the partial repressurization step, in which valves 8, 17 and 29 are closed and valves 5 and 15 are opened to operate blower 2 under no load. The control valve 22 is opened to the set valve position. During the second stage, the partial depressurization stage, the void gas collected in the equalization tank 23 causes the vessel of the adsorbent bed 19 to reach an intermediate pressure level of, for example, 10 psia (0.7 kg / cm ² ) during this partial repressurization stage. Used to repressurize. The pressure in the equalization tank 23 is about 15 in a typical VPSA application.
psia (1.05 kg / cm ² ) to 9.5 psia (0.
67 kg / cm ² ). The time required for this step is substantially the same as the step time required for the partial depressurization step, and is, for example, 4 to 7 seconds. Once the container is repressurized to this intermediate pressure level, the process sequence steps are complete. The cycle proceeds to the first stage, where the process sequence stage is
The continuous operation of the A to VPSA process is repeated as continued with additional feed air.

The approximate pressure levels in the adsorbent bed 19, the product surge tank 26 and the equalization tank 23 at the end of step 5 of the process sequence steps of certain embodiments of the present invention are shown in Table 1 below.

[0021]

[Table 1]

The use of a separate gas equalization tank for the repressurized gas, especially in VPSA process operations,
Product recovery is improved and power requirements are reduced. The gas expelled from the adsorbent bed is collected in the equalization tank when the adsorbent bed vessel is at its upper adsorption pressure and when partial vessel depressurization is initiated. The collected gas is a void gas, which is any gas stored in any of the adsorbent gaps in the vessel resulting from the gaps between the adsorbent particles and desorbed from the adsorbent surface when the bed pressure is reduced. It is nitrogen gas. The purity of the void gas in the equalization tank is nitrogen desorbed from a portion of the gas collected in the equalization tank, so the void gas has a high nitrogen concentration, and therefore the purity in the product surge tank is Are different. Generally, the oxygen purity in the equalization tank is about 85-89.
%, Which is in contrast to the higher purity of 90-93% oxygen typical of the product gas in the product surge tank. When the adsorbent bed vessel is exhausted and at a pressure level below atmospheric pressure, the vessel is approximately 10 psi with void gas from this equalization or holding tank.
Partially repressurized to a pressure of a (0.7 kg / cm ² ).
By recirculating the void gas from the partial depressurization stage, rather than blowing it down to atmospheric pressure as in prior art schemes, more of the oxygen molecules fed to the system can be recovered. , Improve product recovery. This increase in product recovery means that the product oxygen flow rate increases for the same inlet gas flow rate. This increase in product flow rate results in reduced unit power consumption for the PSA system. The incorporation of the equalization tank into the PSA, and in particular into the VPSA, thus serves to improve product recovery and save unit power at the relatively low cost of the equalization tank, providing two important benefits.

Another beneficial feature of the present invention is the use of product oxygen from the product tank as a purge gas during the exhaust phase. The adsorbent bed vessel is, for example, a partial vacuum (subatmosph
eric), the nitrogen gas adsorbed on the surface of the adsorbent desorbs due to the partial pressure difference. The desorbed nitrogen remains in the space between the adsorbent particles in the container. It is desirable to remove most of such desorbed nitrogen from the adsorbent bed vessel. This is because as soon as the pressure in the container begins to increase, the partial pressurization propels the remaining nitrogen gas in the container back to the surface of the adsorbent for adsorption and the adsorbent is never fully regenerated. . By introducing a purge gas stream containing 90-93% pure oxygen from the product surge tank, the nitrogen gas remaining in the vessel is flushed and replaced with product oxygen gas. When the bed is subsequently repressurized, the void gas consists mainly of oxygen,
It is not adsorbed when the pressure in the vessel begins to rise, keeping the adsorbent surface fully regenerated in preparation for the next feed feeding stage. In general, the higher the oxygen purity of the purge gas, the more effective the purge stage. The reason is that the more nitrogen gas that remains in the vessel, the more gas will be re-adsorbed on the adsorbent during the partial repressurization step, reducing the effectiveness of regeneration of the adsorbent surface. The desired air separation is enhanced when the purge gas introduced into the vessel has the lowest possible nitrogen concentration.

In the practice of the present invention, an improvement in product flow of 20-25% over prior art approaches is realized,
The product gas is thereby used as a repressurized gas source for the adsorbent bed. The use of product gas for repressurization can result in only a very small portion of such product gas being available for downstream use. By using void gas for partial repressurization of the vessel, all of the product gas produced in the process of the present invention is available for the desired downstream use of the product gas. This provides a distinct performance advantage in the art for single bed PSA operation.

In the practice of the present invention, any suitable adsorbent capable of selectively permeating nitrogen from air may be used. For example, well-known molecular sieves such as 5A and 13X zeolite type molecular sieve materials can be used in a conventional manner.

While conventional types of theolite type molecular sieves can be used as adsorbents in the practice of the present invention, a variety of specially modified materials are also available for selective adsorption and delivery of the desired nitrogen to the feed air. It can be used to recover oxygen as a non-adsorbed component of the desired product gas in air. Thus, the adsorbent may be, in certain embodiments, the lithium cation form of zeolite X or a mixed cation form thereof, such as the lithium and calcium forms. It has been found that such lithium X, or LiX, adsorbents exhibit highly desirable capacity and selectivity towards adsorption of nitrogen from other streams containing small polar or less polar species such as air or oxygen. Was issued.

The LiX adsorbent preferably used in the practice of this invention is the lithium cation form of zeolite X, where the framework Si / Al ₂ molar ratio is about 2.0.
3.0, preferably in the range of 2.0 to 2.5 and AlO ₂ - at least about 88% of the tetrahedral unit, preferably at least 90%, more preferably at least 95% is associated with lithium cations There is. The nitrogen adsorption performance of such highly ion-exchanged LiX is
It is completely unpredictable from the results obtained using a LiX material where less than 86 equivalents of cation is lithium and the balance is predominantly sodium cation. Further, in the relative proportion of AlO ₂ -tetrahedral units in the zeolite X skeleton, the total tetrahedral unit is 44.4.
% To 50% of the total unit and the associated increase in Li ⁺ ions, ie the same equivalent% of the same Li ⁺ ion in each case is the adsorption capacity of the zeolite for nitrogen and the number of cations in the LiX material of selectivity. It has been found to play a significantly greater role than just related to the shown increase in.

LiX for use in the practice of the present invention
Conventionally available zeolite X starting materials can be readily used in the preparation of the materials. Two such materials have predominantly sodium cations, 2.5 and 2.
Zeolite X having a SiO ₂ / Al ₂ O ₃ ratio of 0, a NaX material. 2.5NaX material is described in US Pat. No. 2,88.
Approximately 100 using sodium silicate and sodium aluminate and water as reagents according to the teachings of 2,244.
It can be synthesized hydrothermally at a temperature of ° C. The reaction mixture has the following composition expressed in oxide molar ratio: 3.5Na ₂ O: Al ₂ O ₃ :
3.0SiO ₂ : 144H ₂ O

The 2.0NaX material can be synthesized in the mixed sodium-potassium form. For example, first, 267g of 5
208 using heating and stirring in 0% aqueous NaOH
g Al (OH) ₃ is dissolved to form a first solution, solution (a). Solution (b) is 2 g in 1000 g water.
Prepared by dissolving 87 g of 85.3% KOH pellets and mixing the solution thus formed with 671 g of 50% aqueous NaOH. Solution (a) is gradually added to solution (b) to form solution (c), which is cooled to 4-12 ° C. 453.25 g of solution (d)
40 grade sodium silicate (9.6% Na ₂ O, 30.
9% SiO ₂ ) is prepared by diluting with 131.7 g of water. The cooled solution (c) is added to the solution (d) in a mixer and mixed at low speed for 3 minutes. Cooling and avoiding the generation of unequal amounts of mechanical energy in the final mix are important factors in the preparation of high quality products. Gelation should not occur until after about 4 minutes. The gel is placed at 36 ° C for 2-3 days and aged at 70 ° C for 16 hours. The desired zeolite is then isolated by filtration and the filter cake is washed with aqueous NaOH solution (pH: 12) in an amount corresponding to 7 times the volume of the mother liquor.
The washed product was washed with 4 l of NaOH aqueous solution (pH: 1
Reslurry in 0), collect by filtration and wash with water. The reslurry process is preferably repeated two or more times and the isolated product is air dried.
The dried product was slurried in 100 ml of 1% NaOH solution and 21% at 90 ° C. in the slurry.
Maintained for hours. After filtration, the cake is 1000 ml N
It is reslurried with an aOH solution (pH: 12) at 60 ° C. for 30 minutes and filtered. The reslurry process is desirably repeated two more times and the post-solids are collected by filtration, washed with aqueous NaOH (pH: 9) and post-air dried.

Using 2.5NaX as prepared as described above, the zeolite "preformed" agglomerates initially had a pH of 12 starting zeolite crystals and were essentially free from sodium hydroxide and water. Can be produced by washing with an aqueous caustic solution and then with water to a pH of 9. The washed zeolite crystals are then mixed with Avery clay-a commercially available kaolin-type clay-at a ratio of 80 wt% zeolite and 20 wt% clay. The zeolite-clay mixture is then mixed with a sufficient amount of water to produce an extrudable material with sufficient green strength to allow the extruded pellets to undergo a sufficient firing step. In the firing stage,
Kaolin chamber clay is converted to the active metakaolin form in about 1 hour at about 650 ° C. After calcination, the bound agglomerates are cooled and soaked and aged in caustic aqueous solution at about 100 ° C. to give a bulk of metakaolin, mainly zeolite X.
Converts to crystalline zeolite crystals. The aged agglomerates were removed from the caustic aging solution and re-pHed to 9-10.
Washed with fresh aqueous NaOH solution and air dried. The dried product pellets are crushed and 1
Sieve to have a particle morphology with convenient dimensions such as 6x40 mesh.

The particles of such a mesh can be activated by heating in vacuum at a temperature of 375 ° C. for about 2.5 hours. This activation is carried out carefully in this manner so that the zeolite NaX crystals are not subjected to the severe hydrothermal action by the water vapor formed from the occluded and / or adsorbed water. The activation material thus formed is 2.5NaX activation material.

In the preparation of the LiX material, the unactivated particles of a given mesh had a particle size of 1.0 adjusted to a pH of 9.0 using LiOH in a glass column.
It may be subjected to an ion exchange process so as to be contacted by a stream of molar aqueous lithium chloride at a temperature of 80 ° C. The amount of lithium chloride solution is used so that it is desirably contacted with a 4-fold stoichiometric excess of lithium ions for about 14 hours. The ion exchange solution flowing out of the column is not recycled. The resulting ion-exchanged product is washed with water and adjusted to a pH of 9 using LiOH and in this case 94% ion-exchanged.

Low silica 2.0 prepared as described above
Using NaKX material, the alkali metal cations can be replaced by lithium cations if desired by ion exchange using aqueous lithium chloride (pH: 9, adjusted with LiOH) to greater than 99 equivalent%. This material comprises 2.0 LiX (99%) material in powder form.

Those skilled in the art will appreciate that in the LiX preparation process and in the preparation of mixed cation adsorbents, these do not form part of the present invention for improved PSA methods and apparatus, although various changes in the details and Understand that it can be modified. With this understanding,
For example, 2.5 NaX material has 4 times the amount of LiC so that products with varying amounts of lithium cations are formed.
It should be noted that it can be ion-exchanged with lithium chloride (pH: 9, adjusted using LiOH) using either more or less than 1 and the volumetric technique described above. It will also be appreciated that the desired LiX material can be prepared by such ion exchange using lithium carbonate or other seed lithium salt instead of lithium chloride. Similarly, the LiX material or Li that constitutes the desired adsorbent for use in certain embodiments of the present invention.
The mixed cation materials, such as CaX materials, may have practical operational requirements for a given application, such as specific feed gas or product gas pressure to temperature conditions and / or the desired separation and recovery associated with the given application. It can be used under various operating conditions corresponding to the level.

Many other changes can be made in the details of the invention without departing from the scope of the invention. Cylindrical adsorbent vessels with shallow dish heads above and below are commonly used with an axial gas flow therethrough, but otherwise the gas flow is radial, i.e. Adsorbent vessels adapted to enter the outer cylinder perimeter and into the inner cylinder where the product stream is collected can be used. Since the flow area is a variable-area cross-section flow path, the pressure losses associated with the flow are thereby reduced, and thus further power consumption savings can be obtained. In addition, the axial length of the adsorbent vessel can be made very long in order to store a larger amount of adsorbent and produce more product, but the flow path length is kept at the radius of the vessel, Therefore, the pressure drop associated with radial flow does not change. Based on 1000 lbs (450 kg) molecular sieve / TPD bed size factor (BSF), the flow range for this type of vessel configuration is 1 in the adsorbent vessel.
5,000-80,000 pounds (6750-3600)
0 kg) molecular sieve adsorbent 15,
000-80,000 NCFH (420-2240 m ³
/ Hour: Standard state) oxygen flow rate range.

It should be noted that VPSA plants using lithium exchange adsorbents work very well even in warm weather conditions when the feed temperature can be controlled with cooling water in the feed aftercooler. However, in cold weather, when the ambient temperature is near or below freezing, the temperature of the adsorbent decreases and the performance of the adsorbent using the lithium exchange adsorbent appears to decrease. In order to increase the temperature in the adsorbent vessel, the feed air into the vessel can be heated to a level close to the temperature involved during warm ambient conditions. This may be achieved by adding a preheater at the inlet to the blower instead of the feed aftercooler in climates where ambient temperatures in summer do not exceed 24-27 ° C.

In order to make the product flow unit more cost effective, the aftercooler and preheater features may be eliminated from certain embodiments of the present invention. The varying ambient conditions and the resulting reduction in product recovery due to vessel temperature may not be significant enough to warrant additional use of such components in PSA to VPSA systems. It is also within the scope of the invention to eliminate the use of an inlet air muffler / buffer tank. This exclusion is not recommended for large plants due to the pulsating behavior of the gas, but a lower product flow, ie 5
It can be excluded for the range of -10 tons / day.
The combination of supply / exhaust emission silencer or components 9 and 11 also helps to simplify the PSA to VPSA system and provides overall cost savings in a practical industrial embodiment of the invention.

In situations where a higher purity product is desired, the sixth stage, the secondary repressurization stage, may be used. After the vessel receives the repressurized gas at 85-89% oxygen purity from the equalization tank, the sixth step is to introduce higher oxygen gas, eg 90-93% pure, into the cavities of the adsorbent vessel. Take in a small amount of purge gas from the product surge tank. In this manner, the average purity in the voids is increased, and thus higher purity oxygen products achieve such an increase in oxygen product purity, at the expense of some product recovery, but at the product flow rate. Can be produced without a significant decrease in

[0039]

The present invention provides improvements in single bed PSA and VPSA process operation. By achieving an improved product flow rate and increasing the adsorption capacity of a single adsorbent bed, the present invention improves single bed operation and is a low cost single bed PSA and VP for practical air separation operations.
It further enhances the utility of using the SA system.
In practicing the present invention, 20 compared to prior art schemes
A product flow improvement of ~ 25% is achieved whereby the product gas is used as a repressurized gas source for the adsorbent bed.
By introducing a purge gas stream containing 90-93% pure oxygen from the product surge tank, the nitrogen gas remaining in the vessel is flushed and replaced with product oxygen gas. When the bed is subsequently repressurized, the void gas consists mainly of oxygen, which is not adsorbed when the pressure in the vessel begins to rise and the adsorbent surface is fully regenerated in preparation for the next feed feed stage. To keep it in the specified state. The use of product gas for repressurization can result in only a very small portion of such product gas being available for downstream use. Due to the use of void gas for partial repressurization of the vessel, substantially all of the product gas produced in the process of the present invention is available for desired downstream use of the product gas. This provides a distinct performance advantage in the art for single bed PSA operation.

[Brief description of drawings]

1 is a flow chart of a specific embodiment of a single process bed, single machine VPSA system facility for the production of oxygen from air.

[Explanation of symbols]

 1 Pipeline 2 Supply blower / vacuum blower combined use blower unit 3 Dust filter-gas silencer unit 4 Valves 5, 6, 7 Pipeline 8 Valves 9 and 11 Exit snubber unit 10 Pipeline 12 Aftercooler 13 Valve 14 Discharge pipeline 15 , 17 valves 16 pipelines 19 single adsorption bed 20, 21, 24, 27 pipelines 22, 29 valves 23 equalization tank 25 check valve 26 product surge tank

Claims (12)

[Claims] 1. A pressure-changing adsorption method for recovering oxygen from air, which comprises (a) adsorption capable of selectively adsorbing nitrogen as a component in air which can easily adsorb supply air. Passing through the feed end of a single bed of agent material, increasing the pressure in the bed from an intermediate pressure to an upper adsorption pressure, and oxygen as a non-adsorbable component of the air from the product end of the bed Passing through a product surge tank at a pressure close to the upper adsorption pressure, and (b) depressurizing the bed to an intermediate pressure in the same direction as the feed air flow by releasing void gas from the product end of the bed, Passing the gas through an equalization tank; (c) depressurizing the bed from an intermediate pressure to a lower desorption pressure in a counter-current flow to the feed air flow by releasing an additional amount of gas from the bed feed end; ) Product gas from the product surge tank Passing a sidestream of the gas as a purge gas through the product end of the bed to evacuate desorbed nitrogen from the voids of the bed at the lower desorption pressure and release the desorbed desorbed nitrogen from the feed end of the bed; (E) introducing void gas from the equalization tank to the product end of the bed to increase the pressure in the bed from the lower desorption pressure to the intermediate pressure; and (f) supplying an additional amount. Passing air through the feed end of the single bed and continuing the cyclical operation of steps (a)-(e), whereby product oxygen is recovered from the air at an increased product flow rate. And a pressure change adsorption method for recovering oxygen from air, which is characterized by improving the adsorption capacity of a single bed of adsorbent material. 2. The pressure-changing adsorption method according to claim 1, wherein the lower desorption pressure is a partial vacuum pressure. 3. The upper adsorption pressure is above atmospheric pressure and the intermediate pressure is below atmospheric pressure.
Pressure change type adsorption method. 4. The pressure change adsorption method according to claim 1, wherein the adsorbent material is a zeolite type molecular sieve material. 5. A step of passing a small amount of product gas from a product surge tank to the product end of the bed following the introduction of the void gas into the bed in step (e), whereby The pressure change adsorption method according to claim 1, wherein the average purity of oxygen is increased. 6. A pressure change adsorption device for recovering oxygen from supply air, comprising: (a) an adsorbent material capable of selectively adsorbing nitrogen as an easily adsorbable component in air. A single bed of: (b) an equalization tank for holding void gases released from the product end of said bed; (c)
A product surge tank for holding product oxygen released from the product end of the bed, and (d) for passing void gas to the equalization tank and to product oxygen to the product surge tank. And (e) the flow of void gas to the equalization tank and the flow of product oxygen to the product surge tank and the flow of void gas from the equalization tank to the bed product end and the flow of product oxygen. Control means for controlling the flow of the sidestream product surge tank to the bed product end; (f)
Feed blower means for passing air through the feed end of the floor,
(G) conduit means for releasing void gases and nitrogen from the feed end of the bed, whereby product oxygen can be recovered in a pressure swing adsorption device at an increased product flow rate and the adsorbent A pressure-changing adsorption device for the recovery of oxygen from air, characterized in that the adsorption capacity of a single bed of material is improved. 7. The pressure swing adsorption apparatus of claim 6, wherein the means for controlling the flow of product oxygen to the product surge tank comprises a check valve. 8. The pressure swing adsorption apparatus of claim 6, wherein the means for controlling the flow of product oxygen to the product surge tank comprises a pressure control valve. 9. The pressure-changing type adsorption device according to claim 6, wherein the adsorbent material is a zeolite type molecular sieve material. 10. The pressure-change type adsorption device according to claim 9, wherein the adsorbent material is a lithium-type zeolite-type molecular sieve material. 11. The feed blower means is a feed blower and exhaust blower means for withdrawing the void gas and nitrogen from the feed end of the bed to the conduit means for partial void vacuum and nitrogen release. 6 pressure change type adsorption device. 12. The pressure swing adsorption apparatus of claim 6 including an aftercooler downstream of the feed blower means for cooling air passing to the feed end of the bed.